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Rh more satisfactory than the reversed bullet which was only effective at short range. In this they were completely successful, and they produced the K or armour-piercing bullet. This con-. sists of an outer envelope of mild steel of the same size and dimen- sions as the ordinary bullet. In the centre of the envelope is the bullet proper, made of hardened tungsten steel 30 mm. long, 6 mm. in diameter, and pointed at one end. The space between the envelope and the hard bullet is filled with lead. On striking a hard steel plate the outer envelope breaks up, but it and the lead lining appear to perform the function of a cap, and the hardened steel bullet perforates the plate.

At ranges up to 60 yd. with a good rifle, and more than this with a rifle in which the rifling has been worn, the armour-piercing bullet is not effective, owing to unsteadiness in flight, but at longer ranges nothing less than half an inch of the best steel is of any use as a protection against a direct hit at the normal. The action of the armour-piercing bullet, however, differs from that of the reversed bullet. The former is a clean penetration of the plate, whereas the latter punches a hole and removes a portion of the plate in the form of a small cylinder. Both at long and short ranges, therefore, a plate of at least half an inch in thickness was found to be necessary to give any real protection, and as plates of this thickness weigh 20 Ib. per sq. ft. it was obvious that a soldier could not carry his own means of protection in addition to a rifle and the other impedimenta which he took into action. It became necessary then to devise some mechanical method of carrying protection, and the combined efforts of many minds in this direction finally resulted in that weapon of offence and de- fence which was afterwards known as a " tank " (see TANKS).

From the nature of the requirements it will be seen that the practice of the armouring of the tanks was by no means an easy one. In the first place the plates in an untreated condition had to be soft enough to be easily machinable, while after treatment they were required to withstand the penetration of the armour- piercing bullet and the punching action of the reversed bullet. This necessitated a very hard plate, but on the other hand it was essential that they should be sufficiently tough to prevent crack- ing or the breaking off of portions of the plate even when struck near an edge or corner. In addition the plates were to be capable of being riveted to the body of the tank or to one another, and finally they must be of the minimum thickness, as the question of weight was all-important.

These requirements were met by the use of nickel-chrome steel, which possesses properties of hardness and toughness to a remarkable degree. Steel containing 0-3 to 0-5% of carbon with 3 to 4% of nickel and 1-5% to 2-0% of chromium was largely used, and in some cases improved by the addition of one of the rarer metals.

In view of the work which the tanks were designed to carry out it was of the utmost importance that they should be perfectly bullet-proof, and it is perhaps not generally known that every plate was tested by firing trial against the German bullet before it was built into the tank. Under this severe but necessary test a very high degree of excellence in the quality of the plates was attained. The manufacturers had their own rifle ranges where the plates were tested under Government supervision before they were dispatched. (E. F. L.)

ARMSTRONG, SIR WALTER (1850-1918), British art critic and writer, was born in Roxburghshire Feb. 7 1850. He was educated at Harrow and Exeter College, Oxford. On leaving the university he became well known as a writer on art, and his judgment of pictures was considered of great value. From 1880 to 1892 he was art critic to various newspapers, among them being the Pall Mall Gazette, St. James's Gazette and Manchester Guardian. In 1892 he became director of the National Gallery of Ireland, a post which he held for more than twenty years. He was knighted in 1899. Sir Walter Armstrong was more espe- cially an authority on the Dutch 17th-century and English i8th- century periods. He was the author of many works on art, of which the chief are: Gainsborough and his Place in English Art (1898); Sir Joshua Reynolds (1900); J. M. W. Turner (1901); Sir Henry Raeburn (1901) and Art in the British Isles (1909); besides Lives of Alfred Stevens, Peter de Wint, Gainsborough and Velasquez. He was also co-editor of Bryan's Dictionary of Painters. He died in London Aug. 8 1918.

ARMY (see 2.592). In different sections which follow under this heading, the later history and organization of some of the powerful national armies which figured prominently in the World War are dealt with. In the articles on countries details of the post-war organization are given, and the object here is to explain the functioning of their armies in 1914-9.

Command and Administration. In 1910 the British army was commanded and administered by an Army Council, a sys- tem first instituted on Feb. 6 1904. The constitution of this council was: the Secretary of State for War; the chief of the general staff (whose designation was altered in 1909 to that of " chief of the Imperial general staff "); the adjutant-general to the forces; the quartermaster-general to the forces; the master- general of the ordnance; the finance member of the Council; the civil member of the Council (later known July 1916 as " under-secretary of State for War "); and the secretary of the War Office (as secretary). Outside the headquarters staff an inspector-general of the forces was appointed, whose duties were to review generally and to report to the Army Council on the practical results of the policy of that Council; and for that pur- pose to inspect and report upon the training and efficiency of all troops, on the condition of fortifications and defences and generally on the readiness and fitness of the army for war. On Aug. 2 1910 the duties of the inspector-general of the forces were divided between the inspector-general of the home forces and the inspector-general of the overseas forces (the gen- eral officer commanding-in-chief in the Mediterranean). Both appointments lapsed on the outbreak of war in 1914.

The above constitution of the Army Council continued until the outbreak of the war, after which it was varied from time to time by the following additions: the deputy chief of the Imperial general staff (Dec. 1915); the director-general of military aero- nautics (Feb. 1916); the* director-general of movements and railways (Feb. 1917); the surveyor-general of supply (May 1917). The director-general of military aeronautics, who was first appointed in 1913 directly under the Secretary of State, ceased to be a member on the institution of the Air Council on Dec. 21 1917. Another variation took place on Feb. 27 1918, when the permanent British military representative, British section, Supreme War Council of the Allied Governments, was added; but he again was removed on April 20 of the same year.

The assignment of duties varied somewhat under the suc- cessive Orders in Council, but the general principles were as follows: Duties in relation to operations were allotted to the chief of the general staff; those relating to organization, dis- position, personnel, armament and maintenance, to the adjutant- general, quartermaster-general and master-general of the ordnance; those relating to the Territorial Force Associations, the Volunteer Force and War Department lands, to the civil member; finance duties, to the finance member; transportation, to the director-general of movements and railways; business relating to the commercial administration of army supplies, not under the control of the Ministry of Munitions, to the surveyor-general of supply.

In more detail the responsibilities of the military members of Council were as follows: The general staff dealt with the prepara- tions for and the execution of military operations, including the estimates of forces required, the organization and establishments of these forces from the broader aspect, also with all matters connected with military intelligence and questions of staff duties, including training and education. The adjutant-general was responsible for all questions relating to personnel (except that of the Army Service Corps, Army Ordnance Corps, Army Pay Corps and Chaplains Department) and discipline, for organization, establishments in detail, mobilization, recruiting, discharges and for the control of the Army Medical Service. The quartermaster-general was re- sponsible for supplies, transport, clothing and equipment (including personnel and organization), for movements, quartering, remounts and the Army Veterinary Service. The master-general of the